void setup() {
  // put your setup code here, to run once:
pinMode(13, OUTPUT);
}

void loop() {

  analogWrite(13,0); // 0% Brighness
  delay(100);
  analogWrite(13,64); // 25% Brighness
  delay(200);
  analogWrite(13,155); // 50% Brighness
  delay(300);
  analogWrite(13,255); // 75% Brighness
  delay(500);
  // put your main code here, to run repeatedly
}